Not just (6)
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">not just</span>' is the definition.<br/ ><span class="explanation-format__explanation">('unfair' is the opposite to 'just')</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for unfair that I've seen before include "Not just - lacking in beauty" , "deceitful" , "Dirty" , "out of order" , "Weighted" .)
(Other definitions for invalid that I've seen before include "Not true" , "What Bunbury was, permanently" , "patient [found]" , "Nullified" , "One disabled by illness" .)